Journal of Computer Chemistry, Japan
Online ISSN : 1347-3824
Print ISSN : 1347-1767
ISSN-L : 1347-1767
General Papers
Molecular Simulation of Potential Energies, Steric Changes and Substituent Effects in Photochromic Cyclization/Cycloreversion of Three Kinds of Dithienylethenes by MOPAC-PM6 Method
Kenichi SOMEKAWA
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2014 Volume 13 Issue 4 Pages 233-241

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Abstract

Photochromic dithienylethenes are among promising molecular switching systems for future molecular electronics. Experimental data of potential energies and substituent effects in the photochromic cyclization/cycloreversion reactions of three kinds of dithienylethenes were simulated by MOPAC-PM6 methods. The 6π open-ring isomers are types 1, 3(3h and 3m) and 5, and the closed-ring isomers are 2, 4 and 6. The simulations were also compared with them by B3LYP/6-31G and CASSCF (10,10)/6-31G methods.The photocyclization quantum yields (φOC) depending on the distance (RCC) between the reactive carbon atoms in the crystals are close to unity when RCC of 3h(4'-H) and 5 are less than 4 Å. Their dynamic simulations of the ground state and singlet excited state from the stable anti-parallel conformers made the behaviors clear. Frontier orbital interactions of higher singly occupied molecular orbital (HSOMO) etc. of the 6π open-ring systems of the RCC less than 4 Å are inferred to be effective to go to the singlet excited states (3h* and 5*: Rcc ≒ 2.1 Å) for the cyclizations. Photocyclizations of 1 and 3m(4'-Me) of Rcc larger than 4 Å in solution were also rationalized from the easy change of the 6π faces.Cycloreversions from 2 and 4 via their singlet excited states (2*, 4*: Rcc ≒ 1.6 Å) were cleared. The singlet excited state 6* from 6 was not observed except 5*. The phenomenon is inferred to be one evidence of relative high φCO of 6→5 photoreaction.Some better PM6 calculations comparing with B3LYP/6-31G etc. and one correction for the PM6 are also shown.

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© 2014 Society of Computer Chemistry, Japan
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